This talk presents a solution to a problem -- the interior structure of
a rotating black hole -- that has remained outstanding since Kerr
discovered the exterior geometry of a rotating black hole in 1963.
What happens is more complicated and more interesting than the common
wisdom that matter falls to a central singularity where spacetime as
we know it ceases to exist. Rather, relativistic counter-streaming
between ingoing (going forwards in coordinate time) and outgoing
(going backwards in coordinate time) streams at the inner horizon
drives an inflationary instability in which particles are accelerated
to collide at exponentially huge energies, easily reaching and
exceeding the Planck energy. What does Nature do with this remarkable
machine?